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Pain level between clear aligners and fixed appliances: a systematic review

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Objectives: To assess if there is any difference in pain levels between orthodontic treatment with clear aligners or fixed appliances. Materials and methods: An electronic search was completed in PubMed, The Cochrane Database, Web of Science, Scopus, Lilacs, Google Scholar, Clinical Trials, and OpenGrey databases without any restrictions until February 2019. All comparative study types contrasting pain levels between clear aligners and fixed appliances were included. The risk of bias (RoB) was assessed using the Newcastle-Ottawa Scale, ROBINS-I-Tool, or ROB 2.0 according to the study design. The level of evidence was assessed through the GRADE tool. Results: After removal of duplicates, exclusion by title and abstract, and reading the full text, only seven articles were included. Five were prospective non-randomized clinical trials (CCT), one was a cross-sectional study, and one was a randomized clinical trial (RCT). Two studies presented a high RoB, three a moderate RoB, and two a low RoB (including the RCT). A meta-analysis was not performed because of clinical, statistical, and methodological heterogeneity. Most of the studies found that pain levels in patients treated with Invisalign were lower than those treated with conventional fixed appliances during the first days of treatment. Differences disappeared thereafter. No evidence was identified for other brands of clear aligners. Conclusions: Based on a moderate level of certainty, orthodontic patients treated with Invisalign appear to feel lower levels of pain than those treated with fixed appliances during the first few days of treatment. Thereafter (up to 3 months), differences were not noted. Malocclusion complexity level among included studies was mild. Pain is one of many considerations and predictability and technical outcome are more important, mainly considering that the difference does not seem to occur after the first months of the orthodontic treatment.
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R E V I E W Open Access
Pain level between clear aligners and fixed
appliances: a systematic review
Paula Coutinho Cardoso
1
, Daybelis Gonzalez Espinosa
1
, Paulo Mecenas
1
, Carlos Flores-Mir
2
and
David Normando
3*
Abstract
Objectives: To assess if there is any difference in pain levels between orthodontic treatment with clear aligners or
fixed appliances.
Materials and methods: An electronic search was completed in PubMed, The Cochrane Database, Web of Science,
Scopus, Lilacs, Google Scholar, Clinical Trials, and OpenGrey databases without any restrictions until February 2019.
All comparative study types contrasting pain levels between clear aligners and fixed appliances were included. The
risk of bias (RoB) was assessed using the Newcastle-Ottawa Scale, ROBINS-I-Tool, or ROB 2.0 according to the study
design. The level of evidence was assessed through the GRADE tool.
Results: After removal of duplicates, exclusion by title and abstract, and reading the full text, only seven articles
were included. Five were prospective non-randomized clinical trials (CCT), one was a cross-sectional study, and one
was a randomized clinical trial (RCT). Two studies presented a high RoB, three a moderate RoB, and two a low RoB
(including the RCT). A meta-analysis was not performed because of clinical, statistical, and methodological
heterogeneity. Most of the studies found that pain levels in patients treated with Invisalign were lower than
those treated with conventional fixed appliances during the first days of treatment. Differences disappeared
thereafter. No evidence was identified for other brands of clear aligners.
Conclusions: Based on a moderate level of certainty, orthodontic patients treated with Invisalign appear to feel lower
levels of pain than those treated with fixed appliances during the first few days of treatment. Thereafter (up to 3 months),
differences were not noted. Malocclusion complexity level among included studies was mild. Pain is one of many
considerations and predictability and technical outcome are more important, mainly considering that the difference does
not seem to occur after the first months of the orthodontic treatment.
Keywords: Orthodontic appliances, Pain, Invisalign, Malocclusion
Introduction
Pain is a subjective response and presents a large number
of individual variations under the same trigger conditions.
It depends on several factors such as age, sex, individual
pain threshold, emotional state, stress, amount of applied
force, cultural differences, and previous experiences of
pain [1,2]. Pain complaints are a common feature during
orthodontic treatment [3] directly influencing patients
satisfaction [4]. It is one of the main reasons for orthodon-
tic treatment discontinuation [5].
It is well known that during orthodontic treatment
with fixed appliances, it is common to feel pain and dis-
comfort [6], reaching its peak 24 h after arch insertion,
and being almost imperceptible 7 days after [7,8]. How-
ever, the type of the appliances may have an influence
on the pain and discomfort reported by the patients due
to the type of force applied. Removable appliances pro-
duce intermittent forces, which allow the tissues to re-
organize before compressive forces are reapplied [9].
Regarding studies that have evaluated pain levels with
clear aligners compared to fixed appliances, some studies
have found positive [2,10,11] or negativ e[12] results
related to clear aligners.
© The Author(s). 2020 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and
reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to
the Creative Commons license, and indicate if changes were made.
* Correspondence: davidnormando@hotmail.com
3
Faculty of Dentistry, Federal University of Pará (UFPA), Rua Augusto Correa
01, Belém, Pará 66075-110, Brazil
Full list of author information is available at the end of the article
Cardoso et al. Progress in Orthodontics (2020) 21:3
https://doi.org/10.1186/s40510-019-0303-z
When comparing quality of life (QoL) between pa-
tients treated with fixed appliances and Invisalign (Align
Technology, San Jose, CA), it was observed that both
presented similar QoL results, except under the category
of eating and chewing where the aligner group showed
better results [13].
Systematic reviews have evaluated the efficiency of
orthodontic treatment with clear aligners and they sug-
gested that the outcomes are not as accurate as those
with fixed appliances [1416]. On the other hand, treat-
ment done with clear aligners present some advantages
such as overall decreased treatment and chair time in
patients with mild to moderate malocclusions [17]. Be-
sides that, studies have shown that gingival health tends
to be better, based on the periodontal health index, in
patients treated with clear aligners [18,19].
There are controversial findings regarding pain level
during orthodontic treatment with fixed appliances ver-
sus clear aligners. Thus, the aim of this systematic re-
view was to evaluate the level of pain during orthodontic
treatment in patients treated with clear aligners com-
pared with patients treated with fixed appliances.
Material and methods
Protocol and registration
The present systematic review was registered in the
PROSPERO database (http://www.crd.york.ac.uk/PROS-
PERO, PROTOCOL: CRD42019131359) and was done ac-
cording to the Preferred Reporting Items for Systematic
Review and Meta-Analysis (PRISMA) guidelines (www.
prisma-statment.org).
Eligibility criteria
The following criteria were used in the selection of the
articles:
1. Study design: Randomized or non-randomized con-
trolled clinical trials and cross-sectional studies.
2. Population: Adult patients during orthodontic
treatment.
3. Intervention: Patients treated with clear aligners.
4. Comparison: Patients treated with conventional
fixed appliances.
5. Outcome: Pain level.
6. Exclusion criteria: Laboratory studies, clinical trials,
case reports, literature reviews, and studies done
with patients with syndromes and/or craniofacial
deformities were excluded from the research.
Information sources, search strategy, and study selection
There were no restrictions on languages and dates of
publication. The search was completed by two authors
(P.C.C and D.G.E.) until February 2019. The search was
performed in the following databases: Cochrane,
PubMed, Scopus, Google Scholar, Lilacs, Web of Sci-
ence, Clinical Trials, and OpenGrey. Specific search
strategies per database are shown in Appendix 1. A hand
search was also performed.
The included articles were exported to a bibliography
reference manager (Mendeley, version 1.19.4 Elsevier).
In case of disagreement, a third evaluator (D.N) opinion
was consulted.
Data items and collection
The data collection in duplicate was carried out accord-
ing to the following criteria: type of study, sample size,
intervention, assessment of pain, time of evaluation, se-
quence of the archwires and aligners, pain outcomes,
overall outcomes, analgesic consumption and authors
conclusion (Table 1).
RoB/quality assessment in individual studies
For the cross-sectional study, the Newcastle-Ottawa
Scale adapted to cross-sectional studies was used [21].
The evaluation was done by counting stars acquired in
each category (Table 2).
For the evaluation of RoB for the non-randomized clin-
ical trials, the ROBINS-I-tool [22] was used. The evaluated
criteria were divided into pre-intervention, intervention,
and post-intervention categories. The RoB was individu-
ally analyzed for each study and classified as low, moder-
ate, serious, critical, and no information (Table 3).
For the randomized clinical trial, the RoB was per-
formed using Cochrane Collaboration RoB 2.0 tool [23],
analyzing six domains: random sequence generation, allo-
cation concealment, blinding of patients and personnel,
blinding of outcome assessor, incomplete outcome data,
and selective outcome reporting (Table 4).
Summary measures
Clinical heterogeneity was measured assessing the treat-
ment protocol, according to the archwire sequences and
use of the aligners, times of evaluation of pain levels, use
of analgesics during orthodontic treatment, different
prescriptions of the fixed appliances, and other out-
comes such as soft tissue irritation and eating disorders.
The assessment of pain levels was evaluated through a
visual analog scale (VAS).
For continuous outcomes, descriptive statistics, such
as mean differences and standard deviations, were used
to summarize the data from the included studies.
RoB/quality assessment among studies
The quality of evidence of the included studies was
made according to The Grading of Recommendations
Assessment, Development and Evaluation (GRADEpro
Cardoso et al. Progress in Orthodontics (2020) 21:3 Page 2 of 17
Table 1 Extraction of data
Authors,
(year)
Type of
study
(country)
Sample
size, male/female
ratio, and age
(mean ± sd) per
group (age)
Intervention Assessment of
pain
Time of
evaluation
Sequence Pain
outcomes
Overall
outcomes
Other
outcomes
Analgesic consumption Authors
conclusion
Archwire Align
Almasoud
(2018) [10]
Prospective
CCT (Saudi
Arabia)
CG: n= 32, 12M/
20F (23.56 years
± 5.44)
IG: n= 32p,
10M/22F (28.47
years ± 8.17)
CG: Passive
self-ligating
(Damon)
IG: Invisalign
VAS 10 cm 4 h; 24 h;
3rd, and 7th
day
.014
NiTi
Firsts
aligners
Patients
treated with
IG had
significantly
lower pain
level than
did those in
CG at all
timepoints.
The highest
pain level
was 24 h
Higher
numbers of
participants
reported
having pain
at 4 h and
lower
number in
day 7
More
patients in
CG took
analgesics
when
compared
with the IG
Yes (acetaminophen/
paracetamol)
Patients
treated with
Invisalign
observed lower
pain than did
with braces.
of pain was
experienced at
24 h and at
day 7 in both
groups
Flores-mir
et al.
(2018) [13]
Cross-
sectional
(Alberta,
Canada)
CG: n=4,NA
(NA)
IG: n= 81, NA
(NA)
CG:
conventional
fixed
appliance)
IG: Invisalign
DIDL (Dental
Impacts on
Daily Living)
PSQ (Patient
Satisfaction
Questionnaire)
End of
treatment
NA NA Similar
satisfaction
Eating and
chewing: IG
reported a
better
satisfaction
Patient
satisfaction
remained
relatively
similar 6
months
later for the
bracket-type
treatment
No Both groups
treated
patients had
statistically
similar
satisfaction
outcomes,
except for
eating and
chewing
Fujiyama
et al.
(2014) [20]
Prospective
CCT (Ohio)
CG: n= 55, 25M/
35F (26.45 years
± 5.45)
IG
1
:n= 38, 10M/
28F (26.64 years
± 5.69)
IG
2
:n= 52, 19M/
33F (25.24 years
± 6.51)
CG: Edgewise
(straight wire
with .018
slot)
IG
1
: Invisalign
(IG)
IG
2
: Edgewise
+ Invisalign
(EIG)
VAS 10 cm 1°: 60 s, 6 h,
12 h, 17
days
2°: 3 weeks
after
3°: 5 weeks
after
Slot
.018
Use 20
h/day
EG was
significantly
higher than
others
IG was
significantly
than
others
(intensity of
pain, no. of
days,
discomfort)
NA No Invisalign
causes less
pain compared
to the
traditional
edgewise
treatment;
problems such
as tray
deformation
must be
carefully
checked in the
use of
Invisalign.
Mais-
Damois
et al.
(2015)
Prospective
CCT
(Canada)
CG
1
:n= 19, NA
(NA)
CG
2
:n= 20, NA
(NA) 18M/21F
(14.5 years)
IG: n= 31, 11M/
20F (16 years)
CG
1
: Damon
S
CG
2
: Speed
IG: Invisalign
VAS 0 h, 5 h, 24
h, 3rd, 7th,
14th day
-.016NiTi
-.016CuNiTi
-.016× .022
CuNiTi
-.019× .025
CuNiTi
Aligners 1,
4, 7, and 10
Invisalign
group
reported
lower pain
than fixed
appliances
Patients
with
Invisalign
reported
significantly
less tissue
irritation
than
Quality of life
was slightly
affected in
the first phase
higher in CG
than in IG)
Yes
Exclusively
during the
first week
of
treatment
Perception of
pain with
Invisalign was
lower than
with fixed
appliance. This
method of
treatment is an
Changed each 2 weeks
Cardoso et al. Progress in Orthodontics (2020) 21:3 Page 3 of 17
Table 1 Extraction of data (Continued)
Authors,
(year)
Type of
study
(country)
Sample
size, male/female
ratio, and age
(mean ± sd) per
group (age)
Intervention Assessment of
pain
Time of
evaluation
Sequence Pain
outcomes
Overall
outcomes
Other
outcomes
Analgesic consumption Authors
conclusion
Archwire Align
patients
with fixed
brackets
attractive
therapy for
patients
wishing for an
esthetic
treatment.
Miller
et al.
(2007) [11]
Prospective
CCT (USA)
CG: n= 27, 6M/
21F (28.6 years ±
8.7)
IG: n= 33, 11M/
22F (38 years ±
12.4)
CG:
preadjusted
fixed
appliance
(NA)
IG: Invisalign
- Daily diary:
functional,
psychosocial
and pain-
related
(Likert Scale)
- Pain (VAS)
NA NA NA Fixed
appliances
group
reported
more pain
beginning
at day 1
through day
7
Invisalign
and fixed
appliances
reported
decreases in
OHRQL after
treatment
beginning
The fixed
appliances
subjects took
more pain
medication
during days 2
and 3
Yes The Invisalign
subjects
overall OHRQL
was better
than that of
the fixed
appliances
subjects.
Shalish
et al.
(2011) [12]
Prospective
CCT (Israel)
CG
1
:n= 28,
14M/14F (NA)
CG
2
:n= 19, 4M/
15F (NA)
IG: n= 21, 5M/
16 F (NA)
CG
1
: Buccal
group
(straight wire
GAC and
Ormco)
CG
2
: Lingual
group
(Incognito)
IG: Invisalign
group
HRQoL
VAS (pain)
7
consecutive
days and at
day 14
.014NiTi NA Pain levels
decreased
from the 1
to 7 day.
Invisalign
and Lingual
group
Day 1: %
pain in
Invisalign
group;
Day 2:
Lingual
group;
Small % of
buccal
group
reported
severe pain
Oral
dysfunction,
disturbances
in eating,
general
activity,
recovery time:
Lingual
group
Yes
Highest in
the
Lingual
group
(similar to
the buccal
group)
Lingual
appliance was
associated with
more severe
pain and
analgesic
consumption,
the oral and
general
dysfunction,
and the most
difficult and
longest
recovery
White
et al.
(2017) [2]
RCT (USA) CG: n= 18, 6M/
12F (NA)
IG: n= 23, 11M/
12F (NA)
CG: Fixed
clear
appliance
upper arch
(Radiance)
and metal
brackets
lower arch
(Alexander)
IG: Invisalign
VAS (10 cm) Initial
adjustment:
daily diary
for 7
consecutive
days
Subsequent
adjustments
(2):
Daily diary
for 4 days
-.016CuNiTi
-.017× . 025
CuNiTi
-.016× .022SS
-.017× .025SS
Change
each 2 week
and use 22
h/day
1°: higher in
CG;
2° 3°: higher
in CG
Discomfort
was
significantly
higher in
CG during
the 1st
week and
subsequent
adjustments
First 3 days
after
bonding:
more
discomfort
when
chewing
Analgesic
consumption:
higher in CG
in the first
week; 1° and
2° adjustment
no
No in sleep
disturbances
Yes Traditional
fixed
appliances
produced
significantly
more
discomfort
than did
aligners.
Patients
treated with
aligners and
fixed
appliances
reported
significantly
Cardoso et al. Progress in Orthodontics (2020) 21:3 Page 4 of 17
Table 1 Extraction of data (Continued)
Authors,
(year)
Type of
study
(country)
Sample
size, male/female
ratio, and age
(mean ± sd) per
group (age)
Intervention Assessment of
pain
Time of
evaluation
Sequence Pain
outcomes
Overall
outcomes
Other
outcomes
Analgesic consumption Authors
conclusion
Archwire Align
with fixed
appliances.
less discomfort
at subsequent
adjustments
than after the
initial bonding
or appliance
delivery.
CCT non-randomized controlled clinical trial, RCT randomized clinical trial, VAS visual analog scale, OHRQL oral health-related quality of life, NA not available
Cardoso et al. Progress in Orthodontics (2020) 21:3 Page 5 of 17
Guideline Development Tool, available online at grade-
pro.org)[24].
Table 2 Risk of bias of the studies, according to the Newcastle-Ottawa Scale adapted for cross-sectional studies
Selection (maximum 5 stars) Comparability (maximum 2 stars) Outcome (maximum 5 stars) Total score (maximum 10)
Flores-Mir et al. 2018 [13]4 1 3 8
Newcastle-Ottawa Quality Assessment Scale (adapted for cross sectional studies)
Selection (maximum 5 stars):
1. Representativeness of the sample:
a)Truly representative of the average in the target population. * (all subjects or random sampling)
b)Somewhat representative of the average in the target population. * (nonrandom sampling)
c)Selected group of users.
d)No description of the sampling strategy.
2. Sample size:
a) Justified and satisfactory. *
b) Not justified.
3. Non-respondents:
a) Comparability between respondents and non-respondents characteristics is established, and the response rate is satisfactory. *
b) The response rate is unsatisfactory, or the comparability between respondents and non-respondents is unsatisfactory.
c) No description of the response rate or the characteristics of the responders and the non-responders.
4. Ascertainment of the exposure (risk factor):
a) Validated measurement tool. **
b) Non-validated measurement tool, but the tool is available or described.*
c) No description of the measurement tool.
Comparability (maximum 2 stars):
1. The subjects in different outcome groups are comparable, based on the study design or analysis. Confounding factors are controlled.
a) The study controls for the most important factor (select one). *
b) The study control for any additional factor. *
Outcome (maximum 3 stars):
1. Assessment of the outcome:
a) Independent blind assessment. **
b) Record linkage. **
c) Self-report. *
d) No description.
2. Statistical test:
a) The statistical test used to analyze the data is clearly described and appropriate, and the measurement of the association is presented, including confidence
intervals and the probability level (pvalue). *
b) The statistical test is not appropriate, not described or incomplete
Table 3 Risk of bias of included articles
Domain bias Description
Pre-intervention
Bias due to confounding Assessment of baseline in of certain number of participants by age and malocclusion description
Assessment of the method of pain evaluation
Assessment of time of evaluation
Bias in selection of participants into
the study
Assessment of participants eligibility criteria
Evaluation of eligible participants exclusion or difference between the follow-up period
Intervention
Bias in classification of interventions Assessment of the intervention statususe of the aligner was not properly described (change of the
aligner)
Use of additional orthodontic methods to correct malocclusion (ex: MI, elastic)
Use of analgesic
Post-intervention
Bias due to deviations from intended
interventions
Evaluation of the systematic differences between the intervention (group that used the aligner) and the
comparison group when there is no information about the evaluation of the pain
Use of analgesic for pain relief during orthodontic treatment
Bias due to missing data In the event of loss of follow-up, incomplete collection of data and exclusion of participants from the
analysis
Bias in measurement of the outcomes When assessments of pain perception were not reported or were measured with error
When not all the measures established in the different treatment times are presented
When the use of analgesic is mentioned or not
Bias in selection of the reported
results
Selective report of results when the effect of all measurements of results has not been fully reported
Cardoso et al. Progress in Orthodontics (2020) 21:3 Page 6 of 17
Synthesis of results
A meta-analysis was not justifiable because of the large
amount of clinical, statistical, and methodological
heterogeneity.
Results
Study selection and characteristics
A total of 1773 studies were identified in the following
databases: PubMed (663), Cochrane (124), Web of Sci-
ence (68), Scopus (13), Lilacs (2), Google Scholar (895)
Clinical Trials (5), and OpenGrey (3). A manual search
was also undertaken but no articles were found. The
identified articles were exported to the Mendeley Desk-
top (version 1.19.4) reference manager to remove dupli-
cates, and a total of 1625 articles remained after the
duplicates were removed. A flow diagram of the process
of identification, inclusion, and exclusion of studies is
presented in Fig. 1.
The exclusion of articles by title and abstract was done
by two evaluators (PC and DG), and in the end, 29 stud-
ies were selected to be evaluated by full text. Of these,
22 were excluded because 2 were a literature review, 14
did not have a control or an intervention group, 3 failed
to evaluate pain, and 3 were not related to the objectives
of this systematic review (Table 5).
A total of seven studies were finally included. Five
were prospective non-randomized clinical studies [10
12,20,25], one was a cross-sectional study [13], and one
was a randomized clinical trial [2]. The mean age of the
control group (group with fixed appliances) ranged be-
tween 23.56 [10] and 28.6 [11], but four studies [2,12,
13,25] did not report this information. A homogeneity
was observed due the type of aligner used in all studies
(Invisalign aligner); however, different types of fixed ap-
pliances were used as a control group, such as Edgewise
[20], Damon Q (Ormco, Orange, CA) [10,25] (Ormco,
Glendora, CA), Speed [25] (Strite Industries Ltd., On-
tario, Canada), Radiance (American Orthodontics, She-
boygan, WI) in the maxillary arch, and Alexander
(American Orthodontics, Sheboygan, WI) in the man-
dibular arch [2]. One study just reported a use of a
straight-wire appliance from GAC or Ormco [12], and
two studies did not report any information [11,13].
In five studies [2,10,20,25,26], a VAS was used as a
method for evaluating pain level, one study used a ques-
tionnaire at the end of treatment [13], and two studies
used both methods [11,12].
When evaluating follow-up time, six studies [2,1012,
20,25] reported daily evaluations during 1 week until 3
months of follow-up, and only one study evaluated pain
level at the end of treatment [13].
RoB within studies
The Newcastle-Ottawa scale for cross-sectional studies
was applied for one study [13] and was classified with a
good quality of evidence. A lower grade was applied for
the selection domain due to the representativeness of
the sample that was ranked as selected groups of users.
The ROBINS-I-Tool (Risk of Bias in Non-randomized
Studies-of Interventions) was used in five studies [10
12,20,25] (Table 1). Reasons related to increased RoB
included confusing information (description of the mal-
occlusion, method of pain evaluation, and follow-up
time). Only one [10] study presented a low RoB and four
[11,12,20,25] showed a moderate RoB (Table 6). The
major reason for this grading was related to the use of
analgesics and this information was not properly re-
ported (use or not). One study [11] was classified as high
RoB in the intervention domain due to bias in classifica-
tion of interventions, which included the assessment of
the intervention status, use of additional orthodontic
methods to correct, and use of analgesic.
For the randomized clinical trial [2], RoB was evalu-
ated according to the Cochrane Collaboration RoB 2.0
tool, which presented a low RoB in all domains: random
sequence generation, allocation concealment, blinding of
patients and personnel, blinding of outcome assessor, in-
complete outcome data, and selective outcome reporting
(Table 3).
Summary of individual studiesresults
Among all included studies [2,1013,20,25], pain
scores were obtained 24 h after the beginning of treat-
ment, and four included articles reported higher pain
levels for fixed appliances during this period. However,
only one investigation [10] found a statistically signifi-
cant difference. Two others studies [2,11] only reported
a significant difference on day 3 and on day 4. Both
studies reported that pain levels were higher in the
group treated with fixed appliances. During days 57,
only one study [2] observed a significantly higher level of
pain in the patients with fixed appliances, but the high-
est level of pain was on the third day. Two studies [12,
25] evaluated pain on day 14 and reported no significant
Table 4 Risk of bias of included studies
Risk of bias
Study Random sequence
generation
Allocation
concealment
Blinding of patients,
personnel
Blinding of outcome
assessor
Incomplete
outcome data
Selective outcome
reporting
White et al. (2017) [2] Low Low Low Low Low Low
Cardoso et al. Progress in Orthodontics (2020) 21:3 Page 7 of 17
differences (p> 0.05) in pain level between groups. Only
one study [2] performed this evaluation 2 months after
starting treatment, and significant differences were
found only on day 1 (p= 0.045) and day 2 (p= 0.041),
with higher levels of pain in the control groups.
One study [25] compared different prescriptions of
self-ligating appliances, Speed vs Damon, with Invisa-
lign. Statistical differences were found between the
Speed and Invisalign prescription only in the first ac-
tivation, .016NiTi versus first aligner, and in the
fourth phase, .019× .025CuNiTi and tenth
aligner, 3 days after a follow-up appliance. In these
twoevaluations,thegroupthatusedafixedappliance
presented higher levels of pain when compared to the
Invisalign group. Although one paper [12]reporteda
higher pain level for the aligner group for all
Fig. 1 Diagram with number of records at each stage of the review according to PRISMA statement
Cardoso et al. Progress in Orthodontics (2020) 21:3 Page 8 of 17
evaluation times, 24 h and 14 days, no statistically signifi-
cant (p> 0.05) difference was found for any time point.
Five studies [2,1012,25] reported the use of analge-
sics, of which three studies found statistical differences
in time points for 4 h [10](p= 0.001), 24 h [10,25](p=
0.001 and p= 0.025), day 2 [2,25](p= 0.0023 and p<
0.05), and day 3 [11](p= 0.006), and in all these cases,
patients treated with fixed appliances reported a higher
analgesic consumption. Only one study [12] observed
that analgesic use was higher in the Invisalign group,
since they discontinued their use on day 6, which was
different from the control group that stopped their use on
day 4. One study [13] also assessed QoL and patient satis-
faction during orthodontic treatment, finding a statistical
difference only in the evaluation of eating and chewing,
where the Invisalign group presented a better response
than the control group (47% and 24%, respectively).
Soft tissue irritation was reported to be lower in the
Invisalign group in two studies [12,25] as well as the as-
sessments related to eating disorders [12].
Certainty level
The quality of the articles was assessed using the GRADE
system described in Table 7. All timepoints evaluated in the
studies were rated with low certainty of evidence in all CCT
studies [1012,20,25], except for the RCT [2]thatwas
rated with high certainty of evidence. Just one study [13]
was not included in the evaluation because it was a cross-
sectional study and had not made timepoint evaluations.
Synthesis of results and additional analyses
It was not possible to perform a meta-analysis because of
large amount of clinical, methodological, and statistical
Table 5 List of excluded studies (with reason)
Reference Reason for exclusion
Abu Alhaija et al. (2015) No intervention group
Ashkenazi et al. (2014) No intervention group
Bergius et al. (2000) Literature review
Bretz et al. (2018) No intervention group
Caniklioglu et al. (2004) No intervention group
Djeu et al (2014) No pain evaluation
Fetouh (2008) No pain evaluation
Fleming et al. (2009) No intervention group
Kavaliauskiene et al. (2012) No intervention group
Ke et al. (2019) No pain evaluation
Kim (2013) No control group
Mai-Tam (2018) Literature review
Maldotti et al. (2013) No control group
Noll et al. (2017) Study not related with the SR objective
Pacheco-Pereira et al. (2015) Study not related with the SR objective
Phuong (2018) Study not related with the SR objective
Polat (2007) No intervention group
Rakhshan (2015) No intervention group
Salcedo-Bugarín (2018) No intervention group
Scheurer et al. (1996) No intervention group
Sergl et al. (1998) No intervention group
Zealaiy et al. (2018) No intervention group
SR systematic review
Table 6 Risk of bias of the included studies, according to the ROBINS-I tool
Domains
Pre-intervention Intervention Post-intervention
Author Bias due to
confounding
Bias in selection of
participants for the
study
Bias in
classifying
interventions
Bias due to deviations
from intended
interventions
Bias due to
missing
data
Bias to
measuring
outcomes
Bias in
selecting
reported
results
Overall risk
of bias
judgment
Almasoud
(2018)
Low Low Low Moderate Low Low Low Moderate
Fujiyama
et al.
(2014)
Moderate Low Moderate Low Low Low Moderate Moderate
Mais-
Damois
et al.
(2015)
Moderate Low Low Moderate Low Low Moderate Moderate
Miller et al.
(2007)
Moderate High High Moderate Low Low Low High
Shalish
et al.
(2007)
Moderate Moderate Moderate Moderate Low Low Low Moderate
Cardoso et al. Progress in Orthodontics (2020) 21:3 Page 9 of 17
Table 7 Grading system according to GRADEpro
Clear aligners compared to fixed appliances for pain
Certainty assessment Summary of findings
No. of participants
(studies) followed
up
Risk of
bias
Inconsistency Indirectness Imprecision Publication bias Overall
certainty
of
evidence
Study event rates (%) Relative
effect
(95% CI)
Anticipated absolute effects
With fixed
appliances
With clear
aligners
Risk with
fixed
appliances
Risk difference
with clear
aligners
1st, 3rd, and 7th day (follow up: mean 1 days; assessed with VAS scale)
336 (5 non-
randomized
studies)
Serious
a
Serious
a
Not serious Very
serious
b
All plausible residual confounding would reduce the
demonstrated effect dose response gradient
⨁⨁◯◯
low
181
participants
155
participants
Not
estimable
Low
0 per 1.000
2nd, 4th, 5th, and 6th day (follow up: mean 1 days; assessed with VAS score)
234 (3 non-
randomized
studies)
Serious
a
Serious
a
Not serious Very
serious
All plausible residual confounding would reduce the
demonstrated effect dose response gradient
⨁⨁◯◯
low
110
participants
124
participants
Not
estimable
Low
0 per 1.000
14th day (follow up: mean 1 days; assessed with VAS score)
119 (2 non-
randomized
studies)
Serious
c
Serious
c
Not serious Very
serious
b
All plausible residual confounding would reduce the
demonstrated effect dose response gradient
⨁⨁◯◯
low
67
participants
52
participants
Not
estimable
Low
0 per 1.000
21st, 22nd, 23rd, 36th, and 37th day (follow up: mean 1 days; assessed with VAS score)
93 (1 non-
randomized
study)
Not
serious
Very serious
d
Not serious Very
serious
b
All plausible residual confounding would reduce the
demonstrated effect dose response gradient
⨁⨁◯◯
low
55
participants
38
participants
Not
estimable
Low
0 per 1.000
24th, 25th, 26th, 27th, 35th, 38th, 39th 40th, and 41st day (follow up: mean 1 days; assessed with VAS score)
93 (1 non-
randomized
study)
Not
serious
Very serious
d
Not serious Very
serious
b
All plausible residual confounding would reduce the
demonstrated effect dose response gradient
⨁⨁◯◯
low
55
participants
38
participants
Not
estimable
Low
0 per 1.000
Baseline (follow up: mean 1 days; assessed with VAS SCORE)
223 (3 non-
randomized
studies)
Serious
a
Serious
a,c
Not serious Very
serious
b
All plausible residual confounding would reduce the
demonstrated effect dose response gradient
⨁⨁◯◯
low
121
participants
102
participants
Not
estimable
Low
0 per 1.000
Baseline, 1st, 2nd, 14th, 30th, 33rd, 34th, 60th, 61st, 62nd, 63rd, and 64th day (follow up: mean 1 days; assessed with VAS score)
41 (1 RCT) Not
serious
Not serious Not serious Very
serious
b
All plausible residual confounding would reduce the
demonstrated effect dose response gradient
⨁⨁⨁⨁
high
18
participants
23
participants
Not
estimable
Low
0 per 1.000
3rd, 4th, 5th, 6th, 7th, 31st, and 32nd day (follow up: mean 1 days; assessed with VAS score)
41 (1 RCT) Not
serious
Not serious Not serious Very
serious
b
All plausible residual confounding would reduce the
demonstrated effect dose response gradient
⨁⨁⨁⨁
high
18
participants
23
participants
Not
estimable
Low
0 per 1.000
CI confidence interval
a
This will down grade because one article was classified with a serious RoB
b
This will downgrade because the use of analgesic was not properly described and it may mask the real pain reported by the patients
c
This will downgrade because two articles were classified with moderate RoB
d
This will downgrade because one article as classified with a moderate RoB
Cardoso et al. Progress in Orthodontics (2020) 21:3 Page 10 of 17
heterogeneity among the included studies, mainly due to
differences between the archwire sequence in the fixed ap-
pliances and times of change for the aligners. In addition,
attempts were made to contact the authors by email to col-
lect missing data; however, only two of them responded,
and they sent all the data available. Additional information
still was not useful enough to justify a meta-analysis.
Discussion
In recent years, continuous search for esthetic alternatives
and comfortable orthodontic treatment approaches have
been reasons for significant increases in the number of
cases treated with clear aligners. Recent studies have shown
that patients specifically treated with Invisalign were satis-
fied with their esthetic results and showed an improvement
in their QoL, especially when related to their smile and dur-
ing chewing and eating functions analyzed after treatment
[13,27]. However, concerning the efficacy of treatment, re-
cent systematic reviews have suggested that this treatment
modality presents some difficulties on specific orthodontic
movements when compared with fixed appliances such as
in rotation and vertical movements [14], ideal occlusal con-
tacts, torque control, increasing transverse width and reten-
tion [16]. In addition, a study that evaluated the results of
treatments performed with Invisalign and conventional
brackets according to the American Board of Orthodontics
objective classification system showed that treatment with
fixed appliances are relatively superior than the treatment
performed with Invisalign [28].
Despite the fact that fixed appliances have been the most
effective traditional method for orthodontic treatment for
many years and have shown good treatment efficiency, sev-
eral studies have reported the negative side effects of this
technique, especially plaque accumulation and difficulty of
oral hygiene [26,29]. Another important aspect commonly
observed is pain experience and discomfort during ortho-
dontic treatment [30]since9195% of patients experience
some level of pain at different stages of treatment [8].
Pain is provoked by noxious stimuli and is a complex ex-
perience [30]. Therefore, it is important to understand the
pain pattern during orthodontic treatment because pain and
discomfort are two of the main reasons that affect the pa-
tients QoL during treatment [31]. In addition, fear of pain is
one of the main reasons for discouraging orthodontic treat-
ment [32] and previous studies have found that 8% [33]to
30% [34] of patients discontinue orthodontic treatment due
to pain experienced at the early stages of treatment.
Four studies [10,11,13,25] reported higher levels of
pain for the group treated with fixed appliances during the
first 24 h after beginning treatment, which corroborates
with other studies [6,35,36], which show that the highest
levels of pain are found 1 day after inserting initial arch-
wires. Furthermore, the literature also shows that the pain
is more intense during the first 3 days and is slowly
minimized or disappears on the seventh day. This is in
agreement with most of the included studies of this sys-
tematic review [2,10,11,20]. This pattern of pain occurs
due to initial orthodontic forces that cause discomfort due
to compression of the periodontal ligament, leading to is-
chemia, edema [37], and release of inflammatory media-
tors during the first 2448 h [38]. These mediators such
as prostaglandins (e.g., PgE) and interleukins (e.g., IL-1β)
sensitize nociceptors of the periodontal ligament, increas-
ing discomfort. The levels of these mediators found in the
gingival cervical fluid peak 24 h after the onset of ortho-
dontic force and return to the reference values after 7 days
[39]. This explains the pattern of pain observed during the
first week after the application of orthodontic force.
Although the periods of higher and lower pain levels
were similar for the fixed and Invisalign treated groups, in
the present systematic review only one study [12]showed
higher levels of pain for the group treated with aligners.
They reported that this result may have been found due to
a greater mechanical force applied at the beginning of
Invisalign treatment; however, the sequence, time of use,
and period of exchange of the aligners were not described.
Understanding that pain can affect the QoL of the indi-
vidual, which can lead to worsening oral hygiene and have
a psychosocial impact [40], many patients use analgesics for
pain relief caused by orthodontic treatment. In the present
systematic review, five studies reported the use of analgesics
[2,1012,25], and in all of them, the use of analgesics was
similar to the periods of higher and lower pain levels. The
perception of orthodontic pain is due to changes in blood
flow caused by the appliances, and the use of analgesic may
reduce the inflammatory process, consequently reducing
the pain levels [41], although the use of these pain relief
medications may mask the real pain reported by the pa-
tients leading to an uncertain result. Medication intake was
higher in the fixed appliance group than in the Invisalign
group as previously reported in the literature [8,35]. The
fact that patients with fixed appliances take more medica-
tions may underestimate the pain reported by them when
treated with this type of appliance.
However, pain is a subjective process and can be influ-
enced by several factors. Studies show that pain may be
related to the individuals personality and that patients
who have some knowledge about orthodontic treatment
and have more positive attitudes presented lower levels
of pain during treatment [42,43]. Therefore, it is sug-
gested that the professionals inform the patients of any
discomfort that may occur during orthodontic treatment
and guide ways to alleviate it [42].
Knowing that the activation of the fixed appliance is
done once a month and the aligners changed every 15
days, it may be reasonable to think that patients treated
with aligners report lower pain levels at each activation,
but it is felt for a longer period of time. That said, it is
Cardoso et al. Progress in Orthodontics (2020) 21:3 Page 11 of 17
important to point out that few studies have evaluated
pain over a longer period of treatment. A randomized
clinical trial [2] performed this evaluation for 2 months
and observed the pain in the subsequent appointments
was lower in both groups. In the second month of main-
tenance, no statistical difference was observed.
The types of archwires should be taken in account since
they have differences in some mechanical properties such
as low elasticity module and coefficient of attrition, high
resilience, flexibility and elastic recovery, and biocompati-
bility that are important characteristics to stimulate the
adequate tissue response [4446]. A laboratory study
demonstrates that nickel-titanium archwire with addition
of copper (CuNiTi) presented less favorable biologically
deactivation loads compared to the other thermoactivated
NiTi [47] which is consistent with a systematic review and
meta-analyses [48] that found that patients treated with
CuNiTi archwires presented greater levels of pain in the
Likert scale than those patients treated with NiTi.
However, lower levels of pain found in patients treated
with Invisalign may be related to the fact that removable
appliances produce less tension, pressure, sensitivity, and
pain than fixed appliances [49]. This reduced discomfort in
clear aligners may be associated with proinflammatory me-
diatorssuchasIL-1βbecause in the short term, these medi-
ators increase sensitization by triggering receptor-
associated kinases and ion channels, and in the long term,
they persuade the transcriptional upregulation of receptors,
leading to hyperalgesia [50]. So, it is reasonable to state that
removable appliances predisposed to painless responses
due to the intermittent forces when compared to the con-
tinuous forces of the fixed appliances [51]. Furthermore,
they can be removed by the patients themselves for pain re-
lief. In addition, it was hypothesized by one study [12]that
these results among non-randomized investigations should
be evaluated with caution since cases treated with Invisalign
usually have lower rates of irregularity index, and this dif-
ference may influence the patients perception of pain,
which is considered an important bias in the interpretation
of the results. In this systematic review, only two studies [2,
10] considered crowding level as inclusion criteria, and in
both of them, they range from mild to moderate. However,
the other five studies [1113,20,25]didnotdescribeany
information, and none of the included studies reported any
differences in irregularity index between the evaluated
groups. Despite that, there are controversial results about
the correlation between the irregularity index and the per-
ception of pain. Some studies found that there is no correl-
ation [5254], but a recent one found that crowding is a
risk factor, and with each increase in crowding, there is a
1.10 times increase in painful sensation [55].
Another relevant factor is the type of malocclusion in-
cluded in the studies. Some studies did not report inclu-
sion criteria adequately [1113,20], and among those
who reported [2,10,25], all included patients with mild
or moderate malocclusion, Angle Class I malocclusion,
and crowding of up to 5 mm, which may bias the results,
since the more severe the malocclusion, the more it is
related to the psychosocial well-being of the patient in
pain-related scales, psychological discomfort, and social
problems [56].
Overall, the present systematic review showed lower pain
levels for the groups treated with Invisalign during the first
days of treatment. The studiespresentedahighmethodo-
logical quality according to the grading system, with the
RoB varying from moderate [12,20,25] to high in five stud-
ies [11,13], and only two [2,10]ofthestudiespresenteda
low RoB. Pain is one of many considerations, and predict-
ability and technical outcome are more important, mainly
considering that the difference does not seem to occur after
thefirstmonthsoftheorthodontictreatment.
Limitations
There is a high level of heterogeneity in the design of
the studies included in this systematic review. Among
these studies, we observed a great variation in relation to
the types of fixed appliance used, and five different types
were externally funded by companies. In addition, the
sequence of the archwires used and the set of the aligner
was poorly detailed. Both factors can strongly affect the
results found in this systematic review.
Selection of the participants was only randomized in
one study [2] that presented a high certainty of evidence.
In all other studies [1012,20,25], that were classified
with low certainty of evidence, selection was done accord-
ingtotheorderofappearanceofpatientsseekingortho-
dontic treatment, and in some cases, the patient chose
which type of device they wanted to be treated with.
In addition, the use of analgesics was not reported in
all studies. This may be likely a significant confounding
factor since it is well established in the literature that the
use of this drug camouflages the actual levels of pain
produced during orthodontic treatment.
No other clear aligner appliances were studied in the
included studies. No conclusions/suggestions can there-
fore be made about other alternatives.
Conclusion
Orthodontic patients treated with Invisalign appear to re-
port lower levels of pain than those treated with fixed ap-
pliances during the first few days of treatment. However,
the type of malocclusions was not comprehensively de-
scribed which may lead to controversial results. Thereafter
(up to 3 months), differences were not noted. Malocclu-
sion complexity level among included studies was mild.
Based on the level of certainty, the results should be
evaluated with caution, and it is suggested that studies
with better methodological qualities be performed.
Cardoso et al. Progress in Orthodontics (2020) 21:3 Page 12 of 17
Appendix
Table 8 Database and Search Strategy
Database Search Strategy
Pubmed Search ((((((((((Orthodontic Appliances[MeSH Terms]) OR Orthodontic Appliances[Title/Abstract]) OR Appliance, Orthodontic[Title/
Abstract]) AND Appliances, Orthodontic[Title/Abstract]) OR Orthodontic Appliance[Title/Abstract])) OR
(((((((((((((((((((((((((((((Orthodontic Appliances, Fixed[MeSH Terms]) OR Orthodontic Appliances, Fixed[Title/Abstract]) OR Appliance,
Fixed Orthodontic[Title/Abstract]) OR Appliances, Fixed Orthodontic[Title/Abstract]) OR Fixed Orthodontic Appliance[Title/
Abstract]) OR Fixed Orthodontic Appliances[Title/Abstract]) OR Orthodontic Appliance, Fixed[Title/Abstract]) OR Fixed Functional
Appliances[Title/Abstract]) OR Appliance, Fixed Functional[Title/Abstract]) OR Appliances, Fixed Functional[Title/Abstract]) OR
Fixed Functional Appliance[Title/Abstract]) OR Functional Appliance, Fixed[Title/Abstract]) OR Functional Appliances, Fixed[Title/
Abstract]) OR Fixed Retainer[Title/Abstract]) OR Fixed Retainers[Title/Abstract]) OR Retainer, Fixed[Title/Abstract]) OR Retainers,
Fixed[Title/Abstract]) OR Bonded Retainer[Title/Abstract]) OR Bonded Retainers[Title/Abstract]) OR Retainer, Bonded[Title/Abstract])
OR Retainers, Bonded[Title/Abstract]) OR Fixed Appliances[Title/Abstract]) OR Appliance, Fixed[Title/Abstract]) OR Appliances,
Fixed[Title/Abstract]) OR Fixed Appliance[Title/Abstract]) OR Permanent Retainer[Title/Abstract]) OR Permanent Retainers[Title/
Abstract]) OR Retainer, Permanent[Title/Abstract]) OR Retainers, Permanent[Title/Abstract])) OR ((((((((((((((((((((((((((Orthodontic
Appliances, Removable[MeSH Terms]) OR Orthodontic Appliances, Removable[Title/Abstract]) OR Appliance, Removable
Orthodontic[Title/Abstract]) OR Appliances, Removable Orthodontic[Title/Abstract]) OR Orthodontic Appliance, Removable[Title/
Abstract]) OR Removable Orthodontic Appliance[Title/Abstract]) OR Removable Orthodontic Appliances[Title/Abstract]) OR Clear
Dental Braces[Title/Abstract]) OR Brace, Clear Dental[Title/Abstract]) OR Braces, Clear Dental[Title/Abstract]) OR Clear Dental
Brace[Title/Abstract]) OR Dental Brace, Clear[Title/Abstract]) OR Dental Braces, Clear[Title/Abstract]) OR Clear Aligner
Appliances[Title/Abstract]) OR Aligner Appliance, Clear[Title/Abstract]) OR Aligner Appliances, Clear[Title/Abstract]) OR Appliance,
Clear Aligner[Title/Abstract]) OR Appliances, Clear Aligner[Title/Abstract]) OR Clean Dental Braces[Title/Abstract]) OR Brace, Clean
Dental[Title/Abstract]) OR Braces, Clean Dental[Title/Abstract]) OR Clean Dental Brace[Title/Abstract]) OR Dental Brace, Clean[Title/
Abstract]) OR Dental Braces, Clean[Title/Abstract]) OR Invisalign[Title/Abstract]) OR Invisaligns[Title/Abstract])) OR (((Traditional
Brackets[Title/Abstract]) OR Edgewise appliance[Title/Abstract]) OR Passive self-ligating[Title/Abstract]))) AND (((((((((Pain
Perception[MeSH Terms]) OR Pain Perception[Title/Abstract]) OR Pain Perceptions[Title/Abstract]) OR Perception, Pain[Title/
Abstract]) OR Perceptions, Pain[Title/Abstract])) OR (((((((((((((((((((((((((((((((((((((((((((((((Pain Measurement[MeSH Terms]) OR Pain
Measurement[Title/Abstract]) OR Measurement, Pain[Title/Abstract]) OR Measurements, Pain[Title/Abstract]) OR Pain
Measurements[Title/Abstract]) OR Assessment, Pain[Title/Abstract]) OR Assessments, Pain[Title/Abstract]) OR Pain
Assessments[Title/Abstract]) OR Pain Assessment[Title/Abstract]) OR Analgesia Tests[Title/Abstract]) OR Analgesia Test[Title/
Abstract]) OR Test, Analgesia[Title/Abstract]) OR Tests, Analgesia[Title/Abstract]) OR Nociception Tests[Title/Abstract]) OR
Nociception Test[Title/Abstract]) OR Test, Nociception[Title/Abstract]) OR Tests, Nociception[Title/Abstract]) OR McGill Pain
Questionnaire[Title/Abstract]) OR Pain Questionnaire, McGill[Title/Abstract]) OR Questionnaire, McGill Pain[Title/Abstract]) OR
McGill Pain Scale[Title/Abstract]) OR Pain Scale, McGill[Title/Abstract]) OR Scale, McGill Pain[Title/Abstract]) OR Visual Analog Pain
Scale[Title/Abstract]) OR Visual Analogue Pain Scale[Title/Abstract]) OR Analogue Pain Scale[Title/Abstract]) OR Analogue Pain
Scales[Title/Abstract]) OR Pain Scale, Analogue[Title/Abstract]) OR Pain Scales, Analogue[Title/Abstract]) OR Scale, Analogue
Pain[Title/Abstract]) OR Scales, Analogue Pain[Title/Abstract]) OR Analog Pain Scale[Title/Abstract]) OR Analog Pain Scales[Title/
Abstract]) OR Pain Scale, Analog[Title/Abstract]) OR Pain Scales, Analog[Title/Abstract]) OR Scale, Analog Pain[Title/Abstract]) OR
Scales, Analog Pain[Title/Abstract]) OR Formalin Test[Title/Abstract]) OR Formalin Tests[Title/Abstract]) OR Test, Formalin[Title/
Abstract]) OR Tests, Formalin[Title/Abstract]) OR Tourniquet Pain Test[Title/Abstract]) OR Pain Test, Tourniquet[Title/Abstract]) OR
Pain Tests, Tourniquet[Title/Abstract]) OR Test, Tourniquet Pain[Title/Abstract]) OR Tests, Tourniquet Pain[Title/Abstract]) OR
Tourniquet Pain Tests[Title/Abstract])) OR (((((Patient Comfort[MeSH Terms]) OR Patient Comfort[Title/Abstract]) OR Comfort,
Patient[Title/Abstract]) OR Comfort Care[Title/Abstract]) OR Care, Comfort[Title/Abstract])) OR (((((Toothache[MeSH Terms]) OR
Toothache[Title/Abstract]) OR Toothaches[Title/Abstract]) OR Odontalgia[Title/Abstract]) OR Odontalgias[Title/Abstract])) Sort by:
Best Match
Search ((((((((((Orthodontic Appliances[MeSH Terms]) OR Orthodontic Appliances[Title/Abstract]) OR Appliance, Orthodontic[Title/
Abstract]) AND Appliances, Orthodontic[Title/Abstract]) OR Orthodontic Appliance[Title/Abstract])) OR
(((((((((((((((((((((((((((((Orthodontic Appliances, Fixed[MeSH Terms]) OR Orthodontic Appliances, Fixed[Title/Abstract]) OR Appliance,
Fixed Orthodontic[Title/Abstract]) OR Appliances, Fixed Orthodontic[Title/Abstract]) OR Fixed Orthodontic Appliance[Title/
Abstract]) OR Fixed Orthodontic Appliances[Title/Abstract]) OR Orthodontic Appliance, Fixed[Title/Abstract]) OR Fixed Functional
Appliances[Title/Abstract]) OR Appliance, Fixed Functional[Title/Abstract]) OR Appliances, Fixed Functional[Title/Abstract]) OR
Fixed Functional Appliance[Title/Abstract]) OR Functional Appliance, Fixed[Title/Abstract]) OR Functional Appliances, Fixed[Title/
Abstract]) OR Fixed Retainer[Title/Abstract]) OR Fixed Retainers[Title/Abstract]) OR Retainer, Fixed[Title/Abstract]) OR Retainers,
Fixed[Title/Abstract]) OR Bonded Retainer[Title/Abstract]) OR Bonded Retainers[Title/Abstract]) OR Retainer, Bonded[Title/Abstract])
OR Retainers, Bonded[Title/Abstract]) OR Fixed Appliances[Title/Abstract]) OR Appliance, Fixed[Title/Abstract]) OR Appliances,
Fixed[Title/Abstract]) OR Fixed Appliance[Title/Abstract]) OR Permanent Retainer[Title/Abstract]) OR Permanent Retainers[Title/
Abstract]) OR Retainer, Permanent[Title/Abstract]) OR Retainers, Permanent[Title/Abstract])) OR ((((((((((((((((((((((((((Orthodontic
Appliances, Removable[MeSH Terms]) OR Orthodontic Appliances, Removable[Title/Abstract]) OR Appliance, Removable
Orthodontic[Title/Abstract]) OR Appliances, Removable Orthodontic[Title/Abstract]) OR Orthodontic Appliance, Removable[Title/
Abstract]) OR Removable Orthodontic Appliance[Title/Abstract]) OR Removable Orthodontic Appliances[Title/Abstract]) OR Clear
Dental Braces[Title/Abstract]) OR Brace, Clear Dental[Title/Abstract]) OR Braces, Clear Dental[Title/Abstract]) OR Clear Dental
Brace[Title/Abstract]) OR Dental Brace, Clear[Title/Abstract]) OR Dental Braces, Clear[Title/Abstract]) OR Clear Aligner
Appliances[Title/Abstract]) OR Aligner Appliance, Clear[Title/Abstract]) OR Aligner Appliances, Clear[Title/Abstract]) OR Appliance,
Clear Aligner[Title/Abstract]) OR Appliances, Clear Aligner[Title/Abstract]) OR Clean Dental Braces[Title/Abstract]) OR Brace, Clean
Dental[Title/Abstract]) OR Braces, Clean Dental[Title/Abstract]) OR Clean Dental Brace[Title/Abstract]) OR Dental Brace, Clean[Title/
Abstract]) OR Dental Braces, Clean[Title/Abstract]) OR Invisalign[Title/Abstract]) OR Invisaligns[Title/Abstract])) OR (((Traditional
Brackets[Title/Abstract]) OR Edgewise appliance[Title/Abstract]) OR Passive self-ligating[Title/Abstract]))) AND (((((((((Pain
Cardoso et al. Progress in Orthodontics (2020) 21:3 Page 13 of 17
Table 8 Database and Search Strategy (Continued)
Database Search Strategy
Perception[MeSH Terms]) OR Pain Perception[Title/Abstract]) OR Pain Perceptions[Title/Abstract]) OR Perception, Pain[Title/
Abstract]) OR Perceptions, Pain[Title/Abstract])) OR (((((((((((((((((((((((((((((((((((((((((((((((Pain Measurement[MeSH Terms]) OR Pain
Measurement[Title/Abstract]) OR Measurement, Pain[Title/Abstract]) OR Measurements, Pain[Title/Abstract]) OR Pain
Measurements[Title/Abstract]) OR Assessment, Pain[Title/Abstract]) OR Assessments, Pain[Title/Abstract]) OR Pain
Assessments[Title/Abstract]) OR Pain Assessment[Title/Abstract]) OR Analgesia Tests[Title/Abstract]) OR Analgesia Test[Title/
Abstract]) OR Test, Analgesia[Title/Abstract]) OR Tests, Analgesia[Title/Abstract]) OR Nociception Tests[Title/Abstract]) OR
Nociception Test[Title/Abstract]) OR Test, Nociception[Title/Abstract]) OR Tests, Nociception[Title/Abstract]) OR McGill Pain
Questionnaire[Title/Abstract]) OR Pain Questionnaire, McGill[Title/Abstract]) OR Questionnaire, McGill Pain[Title/Abstract]) OR
McGill Pain Scale[Title/Abstract]) OR Pain Scale, McGill[Title/Abstract]) OR Scale, McGill Pain[Title/Abstract]) OR Visual Analog Pain
Scale[Title/Abstract]) OR Visual Analogue Pain Scale[Title/Abstract]) OR Analogue Pain Scale[Title/Abstract]) OR Analogue Pain
Scales[Title/Abstract]) OR Pain Scale, Analogue[Title/Abstract]) OR Pain Scales, Analogue[Title/Abstract]) OR Scale, Analogue
Pain[Title/Abstract]) OR Scales, Analogue Pain[Title/Abstract]) OR Analog Pain Scale[Title/Abstract]) OR Analog Pain Scales[Title/
Abstract]) OR Pain Scale, Analog[Title/Abstract]) OR Pain Scales, Analog[Title/Abstract]) OR Scale, Analog Pain[Title/Abstract]) OR
Scales, Analog Pain[Title/Abstract]) OR Formalin Test[Title/Abstract]) OR Formalin Tests[Title/Abstract]) OR Test, Formalin[Title/
Abstract]) OR Tests, Formalin[Title/Abstract]) OR Tourniquet Pain Test[Title/Abstract]) OR Pain Test, Tourniquet[Title/Abstract]) OR
Pain Tests, Tourniquet[Title/Abstract]) OR Test, Tourniquet Pain[Title/Abstract]) OR Tests, Tourniquet Pain[Title/Abstract]) OR
Tourniquet Pain Tests[Title/Abstract])) OR (((((Patient Comfort[MeSH Terms]) OR Patient Comfort[Title/Abstract]) OR Comfort,
Patient[Title/Abstract]) OR Comfort Care[Title/Abstract]) OR Care, Comfort[Title/Abstract])) OR (((((Toothache[MeSH Terms]) OR
Toothache[Title/Abstract]) OR Toothaches[Title/Abstract]) OR Odontalgia[Title/Abstract]) OR Odontalgias[Title/Abstract]))
Final search: #1 AND #2
Scopus ( ( ( TITLE-ABS-KEY ( orthodontic AND appliances* ) OR TITLE-ABS-KEY ( "Appliance, Orthodontic" ) OR TITLE-ABS-KEY ( "Appliances,
Orthodontic" ) OR TITLE-ABS-KEY ( "Orthodontic Appliance" ) ) ) OR ( ( TITLE-ABS-KEY ( orthodontic AND appliances, AND fixed* )
OR TITLE-ABS-KEY ( "Appliance, Fixed Orthodontic" ) OR TITLE-ABS-KEY ( "Appliances, Fixed Orthodontic" ) OR TITLE-ABS-KEY (
"Fixed Orthodontic Appliance" ) OR TITLE-ABS-KEY ( "Fixed Orthodontic Appliances" ) OR TITLE-ABS-KEY ( "Orthodontic Appliance,
Fixed" ) OR TITLE-ABS-KEY ( "Fixed Functional Appliances" ) OR TITLE-ABS-KEY ( "Appliance, Fixed Functional" ) OR TITLE-ABS-KEY (
"Appliances, Fixed Functional" ) OR TITLE-ABS-KEY ( "Fixed Functional Appliance" ) OR TITLE-ABS-KEY ( "Functional Appliance,
Fixed" ) OR TITLE-ABS-KEY ( "Functional Appliances, Fixed" ) OR TITLE-ABS-KEY ( "Fixed Retainer" ) OR TITLE-ABS-KEY ( "Fixed
Retainers" ) OR TITLE-ABS-KEY ( "Retainer, Fixed" ) OR TITLE-ABS-KEY ( "Retainers, Fixed" ) OR TITLE-ABS-KEY ( "Bonded Retainer" )
OR TITLE-ABS-KEY ( "Bonded Retainers" ) OR TITLE-ABS-KEY ( "Retainer, Bonded" ) OR TITLE-ABS-KEY ( "Retainers, Bonded" ) OR
TITLE-ABS-KEY ( "Fixed Appliances" ) OR TITLE-ABS-KEY ( "Appliance, Fixed" ) OR TITLE-ABS-KEY ( "Appliances, Fixed" ) OR TITLE-
ABS-KEY ( "Fixed Appliance" ) OR TITLE-ABS-KEY ( "Permanent Retainer" ) OR TITLE-ABS-KEY ( "Permanent Retainers" ) OR TITLE-
ABS-KEY ( "Retainer, Permanent" ) OR TITLE-ABS-KEY ( "Retainers, Permanent" ) ) ) OR ( ( TITLE-ABS-KEY ( orthodontic AND
appliances, AND removable* ) OR TITLE-ABS-KEY ( "Appliance, Removable Orthodontic" ) OR TITLE-ABS-KEY ( "Appliances,
Removable Orthodontic" ) OR TITLE-ABS-KEY ( "Orthodontic Appliance, Removable" ) OR TITLE-ABS-KEY ( "Removable Orthodontic
Appliance" ) OR TITLE-ABS-KEY ( "Removable Orthodontic Appliances" ) OR TITLE-ABS-KEY ( "Clear Dental Braces" ) OR TITLE-ABS-
KEY ( "Brace, Clear Dental" ) OR TITLE-ABS-KEY ( "Braces, Clear Dental" ) OR TITLE-ABS-KEY ( "Clear Dental Brace" ) OR TITLE-ABS-
KEY ( "Dental Brace, Clear" ) OR TITLE-ABS-KEY ( "Dental Braces, Clear" ) OR TITLE-ABS-KEY ( "Clear Aligner Appliances" ) OR TITLE-
ABS-KEY ( "Aligner Appliance, Clear" ) OR TITLE-ABS-KEY ( "Aligner Appliances, Clear" ) OR TITLE-ABS-KEY ( "Appliance, Clear
Aligner" ) OR TITLE-ABS-KEY ( "Appliances, Clear Aligner" ) OR TITLE-ABS-KEY ( "Clear Aligner Appliance" ) OR TITLE-ABS-KEY (
"Clean Dental Braces" ) OR TITLE-ABS-KEY ( "Brace, Clean Dental" ) OR TITLE-ABS-KEY ( "Braces, Clean Dental" ) OR TITLE-ABS-KEY (
"Clean Dental Brace" ) OR TITLE-ABS-KEY ( "Dental Brace, Clean" ) OR TITLE-ABS-KEY ( "Dental Braces, Clean" ) OR TITLE-ABS-KEY (
"Invisalign" ) OR TITLE-ABS-KEY ( "Invisaligns" ))))AND(TITLE-ABS-KEY ( "invisalign" ) ) AND ( TITLE-ABS-KEY ( "pain" ) )
Web of Science ( ( TITLE-ABS-KEY ( orthodontic AND appliances* ) OR TITLE-ABS-KEY ( "Appliance, Orthodontic" ) OR TITLE-ABS-KEY ( "Appliances,
Orthodontic" ) OR TITLE-ABS-KEY ( "Orthodontic Appliance" ) ) ) OR ( ( TITLE-ABS-KEY ( orthodontic AND appliances, AND fixed* )
OR TITLE-ABS-KEY ( "Appliance, Fixed Orthodontic" ) OR TITLE-ABS-KEY ( "Appliances, Fixed Orthodontic" ) OR TITLE-ABS-KEY (
"Fixed Orthodontic Appliance" ) OR TITLE-ABS-KEY ( "Fixed Orthodontic Appliances" ) OR TITLE-ABS-KEY ( "Orthodontic Appliance,
Fixed" ) OR TITLE-ABS-KEY ( "Fixed Functional Appliances" ) OR TITLE-ABS-KEY ( "Appliance, Fixed Functional" ) OR TITLE-ABS-KEY (
"Appliances, Fixed Functional" ) OR TITLE-ABS-KEY ( "Fixed Functional Appliance" ) OR TITLE-ABS-KEY ( "Functional Appliance,
Fixed" ) OR TITLE-ABS-KEY ( "Functional Appliances, Fixed" ) OR TITLE-ABS-KEY ( "Fixed Retainer" ) OR TITLE-ABS-KEY ( "Fixed
Retainers" ) OR TITLE-ABS-KEY ( "Retainer, Fixed" ) OR TITLE-ABS-KEY ( "Retainers, Fixed" ) OR TITLE-ABS-KEY ( "Bonded Retainer" )
OR TITLE-ABS-KEY ( "Bonded Retainers" ) OR TITLE-ABS-KEY ( "Retainer, Bonded" ) OR TITLE-ABS-KEY ( "Retainers, Bonded" ) OR
TITLE-ABS-KEY ( "Fixed Appliances" ) OR TITLE-ABS-KEY ( "Appliance, Fixed" ) OR TITLE-ABS-KEY ( "Appliances, Fixed" ) OR TITLE-
ABS-KEY ( "Fixed Appliance" ) OR TITLE-ABS-KEY ( "Permanent Retainer" ) OR TITLE-ABS-KEY ( "Permanent Retainers" ) OR TITLE-
ABS-KEY ( "Retainer, Permanent" ) OR TITLE-ABS-KEY ( "Retainers, Permanent" ) ) ) OR ( ( TITLE-ABS-KEY ( orthodontic AND
appliances, AND removable* ) OR TITLE-ABS-KEY ( "Appliance, Removable Orthodontic" ) OR TITLE-ABS-KEY ( "Appliances,
Removable Orthodontic" ) OR TITLE-ABS-KEY ( "Orthodontic Appliance, Removable" )
The Cochrane
Library
#1 (Malocclusion$):ti,ab,kw OR (Malocclusions):ti,ab,kw OR (Tooth Crowding):ti,ab,kw OR (Crowding, Tooth):ti,ab,kw OR
(Crowdings, Tooth):ti,ab,kw (Word variations have been searched)
#2 (Malocclusion$):ti,ab,kw OR (Crossbite):ti,ab,kw OR (Crossbites):ti,ab,kw OR (Cross Bite):ti,ab,kw OR (Bite, Cross):ti,ab,kw
(Word variations have been searched)
#3 (Malocclusion$):ti,ab,kw OR ("Bites, Cross"):ti,ab,kw OR (Cross Bites):ti,ab,kw OR (Angle's Classification):ti,ab,kw OR (Angle
Classification):ti,ab,kw (Word variations have been searched)
#4 (Malocclusion$):ti,ab,kw OR (Angles Classification):ti,ab,kw OR (Classification, Angle's):ti,ab,kw (Word variations have been
searched)
#5 #1 and #2 and #3 and #4
#6 (Adult$):ti,ab,kw OR (Adults):ti,ab,kw (Word variations have been searched)
Cardoso et al. Progress in Orthodontics (2020) 21:3 Page 14 of 17
Table 8 Database and Search Strategy (Continued)
Database Search Strategy
#7 (Orthodontic Appliances$):ti,ab,kw OR (Appliance, Orthodontic):ti,ab,kw OR (Appliances, Orthodontic):ti,ab,kw OR
(Orthodontic Appliance):ti,ab,kw (Word variations have been searched)
#8 (Orthodontic Appliances, Fixed$):ti,ab,kw OR (Appliance, Fixed Orthodontic):ti,ab,kw OR (Appliances, Fixed Orthodontic):ti,ab,
kw OR (Fixed Orthodontic Appliance):ti,ab,kw OR (Fixed Orthodontic Appliances):ti,ab,kw (Word variations have been searched)
#9 (Orthodontic Appliances, Fixed$):ti,ab,kw OR (Orthodontic Appliance, Fixed):ti,ab,kw OR (Fixed Functional Appliances):ti,ab,
kw OR (Appliance, Fixed Functional):ti,ab,kw OR (Appliances, Fixed Functional):ti,ab,kw (Word variations have been searched)
#10 (Orthodontic Appliances, Fixed$):ti,ab,kw OR (Fixed Functional Appliance):ti,ab,kw OR (Functional Appliance, Fixed):ti,ab,kw
OR (Functional Appliances, Fixed):ti,ab,kw OR (Fixed Retainer):ti,ab,kw (Word variations have been searched)
#11 (Orthodontic Appliances, Fixed$):ti,ab,kw OR (Fixed Retainers):ti,ab,kw OR (Retainer, Fixed):ti,ab,kw OR (Retainers, Fixed):ti,
ab,kw OR (Bonded Retainer):ti,ab,kw (Word variations have been searched)
#12 (Orthodontic Appliances, Fixed$):ti,ab,kw OR (Bonded Retainers):ti,ab,kw OR (Retainer, Bonded):ti,ab,kw OR (Retainers,
Bonded):ti,ab,kw OR (Fixed Appliances):ti,ab,kw (Word variations have been searched)
#13 (Orthodontic Appliances, Fixed$):ti,ab,kw OR (Appliance, Fixed):ti,ab,kw OR (Appliances, Fixed):ti,ab,kw OR (Fixed
Appliance):ti,ab,kw OR (Permanent Retainer):ti,ab,kw (Word variations have been searched)
#14 (Orthodontic Appliances, Fixed$):ti,ab,kw OR (Permanent Retainers):ti,ab,kw OR (Retainer, Permanent):ti,ab,kw OR
(Retainers, Permanent):ti,ab,kw (Word variations have been searched)
#15 #8 #9 #10 #11 #12 #13 #14
#16 (Orthodontic Appliances, Removable$):ti,ab,kw OR (Appliance, Removable Orthodontic):ti,ab,kw OR (Appliances, Removable
Orthodontic):ti,ab,kw OR (Orthodontic Appliance, Removable):ti,ab,kw OR (Removable Orthodontic Appliance):ti,ab,kw (Word
variations have been searched)
#17 (Orthodontic Appliances, Removable$):ti,ab,kw OR (Removable Orthodontic Appliances):ti,ab,kw OR (Clear Dental Braces):ti,
ab,kw OR (Brace, Clear Dental):ti,ab,kw OR (Braces, Clear Dental):ti,ab,kw (Word variations have been searched)
#18 (Orthodontic Appliances, Removable$):ti,ab,kw OR (Clear Dental Brace"):ti,ab,kw OR (Dental Brace, Clear"):ti,ab,kw OR (Dental
Braces, Clear):ti,ab,kw OR (Clear Aligner Appliances):ti,ab,kw (Word variations have been searched)
#19 (Orthodontic Appliances, Removable$):ti,ab,kw OR (Aligner Appliance, Clear):ti,ab,kw OR (Aligner Appliances, Clear):ti,ab,kw
OR (Appliance, Clear Aligner):ti,ab,kw OR (Appliances, Clear Aligner):ti,ab,kw (Word variations have been searched)
#20 (Orthodontic Appliances, Removable$):ti,ab,kw OR (Clean Dental Brace):ti,ab,kw OR (Dental Brace, Clean):ti,ab,kw OR
(Dental Braces, Clean):ti,ab,kw OR (Invisalign):ti,ab,kw (Word variations have been searched)
#21 (Orthodontic Appliances, Removable$):ti,ab,kw OR (Invisaligns):ti,ab,kw (Word variations have been searched)
#22 #16 #17 #18 #19 #20 #21
#23 (Pain Perception$):ti,ab,kw OR (Pain Perceptions):ti,ab,kw OR (Perception, Pain):ti,ab,kw OR (Perceptions, Pain):ti,ab,kw
(Word variations have been searched)
#24 (Pain Measurement$):ti,ab,kw OR (Measurement, Pain):ti,ab,kw OR (Measurements, Pain):ti,ab,kw OR (Pain Measurements):
ti,ab,kw OR (Assessment, Pain):ti,ab,kw (Word variations have been searched)
#25 (Pain Measurement$):ti,ab,kw OR (Assessments, Pain):ti,ab,kw OR (Pain Assessments):ti,ab,kw OR (Pain Assessment):ti,ab,kw
OR (Analgesia Tests):ti,ab,kw (Word variations have been searched)
#26 (Pain Measurement$):ti,ab,kw OR (Analgesia Test):ti,ab,kw OR (Test, Analgesia):ti,ab,kw OR (Tests, Analgesia):ti,ab,kw OR
(Nociception Tests):ti,ab,kw (Word variations have been searched)
#27 (Pain Measurement$):ti,ab,kw OR (Nociception Test):ti,ab,kw OR (Test, Nociception):ti,ab,kw OR (Tests, Nociception):ti,ab,
kw OR (McGill Pain Questionnaire):ti,ab,kw (Word variations have been searched)
#28 (Pain Measurement$):ti,ab,kw OR (Pain Questionnaire, McGill):ti,ab,kw OR (Questionnaire, McGill Pain):ti,ab,kw OR (McGill
Pain Scale):ti,ab,kw OR (Pain Scale, McGill):ti,ab,kw (Word variations have been searched)
#29 (Pain Measurement$):ti,ab,kw OR (Scale, McGill Pain):ti,ab,kw OR (Visual Analog Pain Scale):ti,ab,kw OR (Visual Analogue
Pain Scale):ti,ab,kw OR (Analogue Pain Scale):ti,ab,kw (Word variations have been searched)
#30 (Pain Measurement$):ti,ab,kw OR (Analogue Pain Scales):ti,ab,kw OR (Pain Scale, Analogue):ti,ab,kw OR (Pain Scales,
Analogue):ti,ab,kw OR (Scale, Analogue Pain):ti,ab,kw (Word variations have been searched)
#31 (Pain Measurement$):ti,ab,kw OR (Scales, Analogue Pain):ti,ab,kw OR (Analog Pain Scale):ti,ab,kw OR (Analog Pain Scales):
ti,ab,kw OR (Pain Scale, Analog):ti,ab,kw (Word variations have been searched)
#32 (Pain Measurement$):ti,ab,kw OR (Pain Scales, Analog):ti,ab,kw OR (Scale, Analog Pain):ti,ab,kw OR (Scales, Analog Pain):ti,
ab,kw OR (Formalin Test):ti,ab,kw (Word variations have been searched)
#33 (Pain Measurement$):ti,ab,kw OR (Formalin Tests):ti,ab,kw OR (Test, Formalin):ti,ab,kw OR (Tests, Formalin):ti,ab,kw OR
(Tourniquet Pain Test):ti,ab,kw (Word variations have been searched)
#34 (Pain Measurement$):ti,ab,kw OR (Tourniquet Pain Tests):ti,ab,kw (Word variations have been searched)
#35 (Pain Measurement$):ti,ab,kw OR (Pain Test, Tourniquet):ti,ab,kw OR (Pain Tests, Tourniquet):ti,ab,kw OR (Test, Tourniquet
Pain):ti,ab,kw OR (Tests, Tourniquet Pain):ti,ab,kw (Word variations have been searched)
#36 #24 #25 #26 #27 #28 #29 #30 #31 #32 #33 #34 #35
#37 (Patient Comfort$):ti,ab,kw OR (Comfort, Patient):ti,ab,kw OR (Comfort Care):ti,ab,kw OR (Care, Comfort):ti,ab,kw (Word
variations have been searched)
#38 (Toothache$):ti,ab,kw OR (Toothaches):ti,ab,kw OR (Odontalgia):ti,ab,kw OR (Odontalgias):ti,ab,kw (Word variations have
been searched)
#39 #5 OR #6
#40 ("Traditional Brackets") OR (Edgewise appliance)OR(Passive self-ligating) (Word variations have been searched)
#41 #7 OR #15 OR #22 OR #40
#42 #23 OR #36 OR # 37 OR #38
#43 #39 AND #41 AND #42
#44 #30 AND #41
#45 #39 AND #42
#46 #41 AND #42
Cardoso et al. Progress in Orthodontics (2020) 21:3 Page 15 of 17
Abbreviations
CCT: Non-randomized clinical trial; GRADE: The Grading of Recommendations
Assessment, Development and Evaluation; PRISMA: Preferred Reporting Items
for Systematic Review and Meta-Analysis; QoL: Quality of life;
RCT: Randomized clinical trial; RoB: Risk of bias; ROBINS-I-Tool: Risk of Bias in
Non-randomized Studies-of Interventions; VAS: Visual analog scale
Acknowledgements
Not applicable
Authorscontributions
PC realized the research and was the major contributor in writing the
manuscript. DGE also realized the research and helped with the writing and
with the all the stages of this article. PM helped with the research and
corrected the writing. CFM corrected the writing and made and contributed
with the correct structure of this article. DN corrected all the steps of this
systematic review and corrected the writing. All authors read and approved
the final manuscript.
Funding
Not applicable
Availability of data and materials
The datasets used and/or analyzed during the current study are available
from the corresponding author on reasonable request.
Ethics approval and consent to participate
Not applicable
Consent for publication
Not applicable
Competing interests
The authors declare that they have no competing interests.
Author details
1
Federal University of Pará (UFPA), Belém, Pará, Brazil.
2
Faculty of Medicine
and Dentistry, University of Alberta, Edmonton, Canada.
3
Faculty of Dentistry,
Federal University of Pará (UFPA), Rua Augusto Correa 01, Belém, Pará
66075-110, Brazil.
Received: 19 September 2019 Accepted: 13 December 2019
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Cardoso et al. Progress in Orthodontics (2020) 21:3 Page 17 of 17
... Although the number of patients treated with orthodontics has increased, treatment-related pain remains a major concern. Several studies have reported that 91% to 95% of patients had pain at the time of orthodontic treatment, regardless of the type of orthodontic appliance [20] [21]. Many studies compared pain experienced with different orthodontic appliances [22] [23] [24]. ...
... Many studies compared pain experienced with different orthodontic appliances [22] [23] [24]. Cardoso et al. [21] found that orthodontic patients treated with Invisalign felt lower levels of pain than those treated with fixed appliances during the first few days of treatment. Thereafter, for up to 3 months, differences were not noted. ...
... Initially, they were only used to treat simple cases (such as mild crowding or diastema closure). Today, they are also widely used for moderately to extremely complex cases, and even in some cases of non-permanent dentition [27,28]. In recent years, the field of neuroscience has played a role in such an assessment through the application of so-called "smart eye-tracking technology". ...
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Smart eye-tracking technology (SEET) that determines visual attention using smartphones can be used to determine the aesthetic perception of different types of clear aligners. Its value as a communication and comprehension tool, in addition to the ethical and legal concerns which it entails, can be assessed. One hundred subjects (50 F, 50 M; age range 15–70) were equally distributed in non-orthodontic (A) and orthodontic (B) groups. A smartphone-based SEET app assessed their knowledge of and opinions on aligners. Subjects evaluated images of smiles not wearing aligners, with/without attachments and with straight/scalloped gingival margins, as a guided calibration step which formed the image control group. Subsequently, the subjects rated the same smiles, this time wearing aligners (experimental images group). Questionnaire data and average values for each group of patients, and images relating to fixation times and overall star scores, were analyzed using these tests: chi-square, t-test, Mann–Whitney U, Spearman’s rho, and Wilcoxon (p < 0.05). One-way ANOVA and related post-hoc tests were also applied. Orthodontic patients were found to be better informed than non-orthodontic patients. Aesthetic perception could be swayed by several factors. Attachments scored lower in aesthetic evaluation. Lips distracted attention from attachments and improved evaluations. Attachment-free aligners were better rated overall. A more thorough understanding as to the opinions, expectations and aesthetic perception of aligners can improve communication with patients. Mobile SEET is remarkably promising, although it does require a careful medicolegal risk–benefit assessments for responsible and professional use.
... In a systematic review that investigated the pain level between aligners and fixed appliances, this issue was criticized, and it was stated that there was a high level of heterogeneity in the design of the studies. 21 The second one is that the individual variations of the participants were not considered while forming the groups in these studies. Pain is a subjective phenomenon and is greatly influenced by individual variations such as age, gender, the amount of dental crowding, the pain threshold, the emotional status of the participant, cultural differences and previous experiences of pain. ...
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The aim of this study was to compare the pain perceived in fixed orthodontic and aligner treatments during the first seven days of treatment. Forty patients who had 3–6 mm maxillary dental crowding and a non-extraction treatment plan were included in this study. The subjects were randomly divided into two groups: the fixed orthodontic group and the aligner group, with ten females and ten males in each. In the fixed orthodontic group, treatment was started with 0.014-inch round nickel-titanium archwire, and a 0.018×0.025-inch preadjusted edgewise appliance was used. In the aligner group, treatment was started with a polyurethane aligner. Throughout the study, teeth in the upper jaw were treated in both groups. The pain scores of the subjects were measured with the visual analog scale at the second and sixth hours and on the first, second, third, and seventh days of treatment. The pain scores of the fixed orthodontic group were significantly higher than those of the aligner group at the sixth hour, on the first, second, and third day. The differences at the second hour and on the seventh day were not statistically significant. According to the study outcomes, less pain was felt during the aligner treatment compared to the fixed orthodontic treatment. However, it should be considered that the force activation interval is shorter in the aligner treatment, and the cumulative pain score may be higher.
... Clear Aligners Treatment (CAT) is widely used, especially in adult patients, due to advantages, such as better periodontal health [1], a lower risk of apical root resorption [2] and white spot lesions [3], comfort and aesthetics [4], a lower pain level [5], and a positive impact on the patient's quality of life [6,7]. Progress in material properties and biomechanical protocols lead also to an acceptable clinical effectiveness in orthodontic movements, such as controlling anterior intrusion, posterior bucco-lingual inclination and molar distalization of approximately 2.5 mm [8]. ...
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The purpose of the present study was to evaluate: (i) maxillary occlusal plane changes after clear aligners therapy with a 3D measurement technique; and (ii) as a secondary outcome, if such changes were correlated to the patient’s 1axilla-mandibular divergence. 3D maxillary models of 32 patients (7 males and 25 females; mean age 22.3 +/− 3.4 year) treated with clear aligners were analyzed. The angle (α) between a reference palatine plane and a maxillary occlusal plane was measured. Five angular cephalometric measurements (NSL/MP; PP-OP; OP-MP; PP-MP; PFH/AFH%) were performed and related to Δα. The subjects were further divided into three groups according to facial divergence. After aligner treatment, Δα increased in hyperdivergent patients and decreased in hypodivergent patients (p < 0.05). Δα showed a significant positive correlation with NSL/MP (rho = 0.44) and negative correlation with PFH/AFH% (rho = −0.53). Aligners treatment produced a counterlockwise rotation of the maxillary occlusal plane, even if this rotation occurs differently depending on divergence.
... is is in line with the findings of a previous work, which found that patient discomfort was reduced in the first few days of treatment, although the differences disappeared after that. [28] Invisalign treatment costs have been discussed in many YouTube testimonials and Twitter posts. [21,29,30] However, most participants in this study did not know the cost of Invisalign treatment, except for those aged 55-64 years, who strongly believed it is less expensive. ...
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Objectives: The demand for clear aligner treatment has increased in recent years. Thus, this study investigated public knowledge regarding Invisalign clear aligner treatment. Material and Methods: A web-based survey was administered through different social media platforms covering different aspects of Invisalign treatment, namely: Treatment efficiency, patient discomfort, appliance esthetic attractiveness, oral hygiene maintenance, and treatment aesthetic results. Participants were also asked to outline their perception of Invisalign treatment cost. A Likert-type scale was used to rank the participant responses. Data were analyzed with the Chi-square test and Bonferroni correction for multiple comparisons. Results: Out of 934 eligible adult participants, 19.6% were aware of Invisalign. Most of the Invisalign-familiar respondents were unaware of its cost (27.9%) but agree it is generally better (49.7%), requires fewer visits (38.2%), results in shorter treatment duration (39.4%) and reduced teeth discomfort (35%), more esthetically attractive (64%), yields easier oral hygiene maintenance (55.2%), and produces superior esthetic results (43.7%) than traditional braces. In addition, males and average-income participants were more likely to believe that Invisalign treatment produces superior esthetic results than traditional braces (P = 0.0002 and P = 0.002, respectively). Average-income participants also believed that Invisalign treatment was generally better (P < 0.0001). While participants in the age-range 55–64 years strongly believe, it is cheaper (P < 0.0001) than traditional braces. Conclusion: This study highlighted the lack of public knowledge about Invisalign treatment. The results also indicated the importance of ensuring public access to reliable information backed up by high-quality evidence.
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Many studies have been undertaken to understand the limitations and benefits of aligners, including systematic reviews with meta-analyses. However, there are very few comprehensive reviews of the current evidence. This literature review provides an up-to-date summary of various aspects of clear aligner therapy, including patient compliance, clinical effectiveness, social interactions and iatrogenic effects. CPD/Clinical Relevance: Clear aligners are a popular choice and the article provides an up-to-date summary of various aspects of clear aligner therapy.
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Full-text available
Objective The objective of this study was to detective the accuracy of model superimposition and automatic analysis for upper and lower dentition width in Invisalign Progress Assessment during the process of clear aligners. Methods 19 cases were included in this study. Pre-treatment dental cast(T0) and post-treatment dental cast after staged treatment(T1) were available for three-dimensional model superimposition. Subsequently, movements of maxillary teeth in horizontal plane (cross section) after staged treatment, width of upper and lower dentition were measured by three-dimensional model superimposition in real world and Invisalign Progress Assessment separately. Consequently, the data collected from these two methods was compared. Results In Invisalign Progress Assessment, movements of maxillary teeth in horizontal plane after staged treatment was 2.31(1.59,3.22) (median (upper quartile, lower quartile)) millimeter (mm), while in three-dimensional model superimposition, the result was 1.79(1.21,3.03)mm. The difference between two groups is significant(P<0.05). Intercanine width upper, intermolar width upper, intercanine width lower, and intermolar width lower were 36.55±2.76mm, 56.98±2.62mm, 28.16±1.85mm, 53.21±2.72mm separately in Invisalign Progress Assessment and were 36.48±2.78mm, 56.89±2.58mm, 28.05±1.85mm, 53.16±2.64mm separately in three-dimensional model analysis, which were no significant difference among these groups (P>0.05). Conclusions The data from Invisalign Progress Assessment was not in parallel with what achieved from model superimposition with palate as reference completely. The accuracy of model superimposition in Invisalign Progress Assessment needs further investigation, whereas the accuracy of model analysis in Invisalign Progress Assessment was accurate. Thereby, results from Invisalign Progress Assessment should be interpreted with caution by the orthodontist in clinic.
Preprint
Full-text available
Objective The objective of this study was to detective the accuracy of model superimposition and automatic analysis for upper and lower dentition width in Invisalign Progress Assessment during the process of clear aligners. Methods 19 cases were included in this study. Pre-treatment dental cast(T0) and post-treatment dental cast after staged treatment(T1) were available for three-dimensional model superimposition. Subsequently, movements of maxillary teeth in horizontal plane (cross section) after staged treatment, width of upper and lower dentition were measured by three-dimensional model superimposition in real world and Invisalign Progress Assessment separately. Consequently, the data collected from these two methods was compared. Results In Invisalign Progress Assessment, movements of maxillary teeth in horizontal plane after staged treatment was 2.31(1.59,3.22)(median (upper quartile, lower quartile)) millimeter (mm), while in three-dimensional model superimposition, the result was 1.79(1.21,3.03)mm. The difference between two groups is significant(P<0.05). Intercanine width upper, intermolar width upper, intercanine width lower, and intermolar width lower were 36.55±2.76mm, 56.98±2.62mm, 28.16±1.85mm, 53.21±2.72mm separately in Invisalign Progress Assessment and were 36.48±2.78mm, 56.89±2.58mm, 28.05±1.85mm, 53.16±2.64mm separately in three-dimensional model analysis, which were no significant difference among these groups (P>0.05). Conclusions The data from Invisalign Progress Assessment was not in parallel with what achieved from model superimposition with palate as reference completely. The accuracy of model superimposition in Invisalign Progress Assessment needs further investigation, whereas the accuracy of model analysis in Invisalign Progress Assessment was accurate. Thereby, results from Invisalign Progress Assessment should be interpreted with caution by the orthodontist in clinic.
Article
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Purpose The purpose of this study was to compare the efficacy of tooth movement between two clear aligner systems by comparing the predicted treatment outcomes versus actual outcomes achieved using a 3D best-fit algorithm. Materials & Methods Clear aligner therapy (CAT) was used to treat 62 patients; n=38 Invisalign® and n=24 Flash®. The Invisalign group had a male to female distribution of 13:25 and a mean age of 35.5, while the Flash group had a male to female distribution of 6:18, with a mean age of 29.2. Differences in predicted versus achieved actual outcomes were compared using eModel Compare 8.1 software. Results 1) Intra-group differences between predicted and achieved tooth movements for angular movements were statistically ( P <0.05) and clinically (>2°) significant with both treatment methods, except for tipping of maxillary and mandibular incisors for Flash® (<2◦). 2) Inter-group results demonstrated statistically significant differences in favor of Flash® for maxillary central incisor Tip (1.3°), BL movements for maxillary canines (0.1mm), and mandibular central incisor Rotations (1°). These did not exceed the threshold for the clinical relevance of 2° or 0.5mm. Conclusions There were no differences in clinical accuracy and efficacy between Invisalign or Flash aligner systems in achieving predicted tooth movement.
Article
Full-text available
Objective: This study proposed to investigate the influence of catastrophizing and others factors related to pain during orthodontic treatment. Methods: 27 patients with 0.022 x 0.028-in Straight-wire brackets were evaluated during alignment and leveling phase with nickel-titanium wires. Visual Analog Scales measured the intensity of orthodontic pain at six moments after a clinical appointment: 6 first hours; 1, 2, 3, 5, and 7 days. Multiple linear regression and stepwise approach assessed the influence of the following variables on pain: catastrophizing, sex, age, duration of treatment, clinical appointment time (morning or afternoon), and wire diameter. Results: The highest pain intensity was reported 24 hours after activation. These data were used to analyze factors associated with pain level. Age (r = 0.062, p= 0.7586), sex (p= 0.28), catastrophizing (r = -0.268, p= 0.1765), and orthodontic wire diameter (r = 0.0245, p= 0.2181) were not correlated with orthodontic pain in the univariate statistics. Catastrophizing was included in the multiple regression model because it was of great interest. Duration of orthodontic treatment (r = 0.6045, p= 0.0008) and the time when orthodontic appliance was activated (p= 0.0106) showed statistical significant associations with pain, and were also included in the multivariate regression, which showed that about 32% of orthodontic pain could be explained by the duration of treatment (R²= 0.32, p= 0.0475). Catastrophizing (R²= 0.0006, p= 0.8881) and clinical appointment time were not significantly associated with pain (R²= 0.037, p= 0.2710). Conclusions: Pain after activation of fixed orthodontic appliance is not associated with catastrophizing as well as age, sex, orthodontic wire diameter, and period of activation.
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We are currently living in an era where the use of computer-aided design/computer-aided manufacturing has allowed individualized orthodontic treatments, but has also incorporated enhanced digitalized technology that does not permit improvisation. The purpose of this systematic review was to analyze publications that assessed the accuracy and efficiency of the Invisalign® system. A systematic review was performed using a search strategy to identify articles that referenced Invisalign®, which were published between August 2007 and August 2017, and listed in the following databases: MEDLINE, Embase, Cochrane Library, Web of Knowledge, Google Scholar, and LILACS. Additionally, a manual search of clinical trials was performed in scientific journals and other databases. To rate the methodological quality of the articles, a grading system described by the Swedish Council on Technology Assessment in Health Care was used, in combination with the Cochrane tool for risk of bias assessment. We selected 20 articles that met the inclusion criteria and excluded 5 due to excess biases. The level of evidence was high. Although it is possible to treat malocclusions with plastic systems, the results are not as accurate as those achieved by treatment with fixed appliances.
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Background Align technology has developed greatly over past few years. Patients tended to prefer clear aligners over conventional brackets because of the superior comfort and esthetics, while the effectiveness of clear aligners was still controversial. The aim of this systematic review was to verify whether the treatment effectiveness of clear aligners was similar to the conventional fixed appliances. Methods A comprehensive search of the Pubmed, Web of Science, Embase, Scopus, and Cochrane Central Register of Controlled Clinical Trials Register databases for studies published through to August 20, 2018 was conducted. Comparative clinical studies assessing the effectiveness of clear aligners compared with braces were included. Results Eight papers were included in this study. Two of the included papers were randomized controlled trials and six were cohort studies. Clear aligners might not be as effective as braces in producing adequate occlusal contacts, controlling teeth torque, increasing transverse width and retention. While no statistically significant difference was found between two groups in Objective Grading System score (WMD = 8.38, 95% CI [− 0.17, 16.93]; P = 0.05). On the other hand, patients treated with clear aligners had a statistically significant shorter treatment duration than with braces (WMD = − 6.31, 95% CI [− 8.37, − 4.24]; P < 0.001). Conclusion Both clear aligners and braces were effective in treating malocclusion. Clear aligners had advantage in segmented movement of teeth and shortened treatment duration, but were not as effective as braces in producing adequate occlusal contacts, controlling teeth torque, and retention.
Article
Full-text available
Background: Aim was to systematically search the literature and assess the available evidence regarding the clinical effectiveness of the Invisalign® system. Methods: Electronic database searches of published and unpublished literature were performed. The reference lists of all eligible articles were examined for additional studies. Reporting of this review was based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Results: Three RCTs, 8 prospective, and 11 retrospective studies were included. In general, the level of evidence was moderate and the risk of bias ranged from low to high, given the low risk of bias in included RCTs and the moderate (n = 13) or high (n = 6) risk of the other studies. The lack of standardized protocols and the high amount of clinical and methodological heterogeneity across the studies precluded a valid interpretation of the actual results through pooled estimates. However, there was substantial consistency among studies that the Invisalign® system is a viable alternative to conventional orthodontic therapy in the correction of mild to moderate malocclusions in non-growing patients that do not require extraction. Moreover, Invisalign® aligners can predictably level, tip, and derotate teeth (except for cuspids and premolars). On the other hand, limited efficacy was identified in arch expansion through bodily tooth movement, extraction space closure, corrections of occlusal contacts, and larger antero-posterior and vertical discrepancies. Conclusions: Although this review included a considerable number of studies, no clear clinical recommendations can be made, based on solid scientific evidence, apart from non-extraction treatment of mild to moderate malocclusions in non-growing patients. Results should be interpreted with caution due to the high heterogeneity.
Article
Full-text available
Objective This study was performed to compare the perception of pain between patients treated with passive self-ligating fixed appliances and those treated with Invisalign aligners. Methods This prospective study conducted in Saudi Arabia used an estimated sample of 64 patients from a private dental clinic. After obtaining written informed consent, the patients were divided into two groups; one group (n = 32) was treated using passive self-ligating fixed appliances and the other group (n = 32) using Invisalign® aligners. Immediately after fitting the appliances, the patients' perception of pain was evaluated through a close-ended and coded self-administrated questionnaire by using a visual analog scale (VAS). Their responses were recorded at 4 hours, 24 hours, day 3, and day 7. Mann-Whitney U-test, Kruskal-Wallis test, and Pearson's chi-square test were performed for statistical analysis. Results A lower percentage of patients treated with Invisalign aligners reported pain than did patients treated with passive self-ligating fixed appliances, and these differences were statistically significant (p = 0.001). Similarly, the mean VAS score for the Invisalign group was significantly lower than that for the passive self-ligating fixed appliance group at different intervals during the first week of treatment. The intensity of pain with both appliances peaked at 24 hours (mean VAS score, 3.87) and was lowest (mean VAS score, 1.62) on day 7. Conclusions During the first week of orthodontic treatment, patients treated with Invisalign aligners reported lower pain than did those treated with passive self-ligating fixed appliances.
Article
Full-text available
Objective: To evaluate differences in discomfort levels between patients treated with aligners and traditional fixed orthodontic appliances. Materials and methods: This blinded, prospective, randomized equivalence two-arm parallel trial allocated 41 adult Class I nonextraction patients to either traditional fixed appliance (6 males and 12 females) or aligner (11 males and 12 females) treatment. Patients completed daily discomfort diaries following their initial treatment appointment, after 1 month and after 2 months. They recorded their levels of discomfort at rest, while chewing, and while biting, as well as their analgesic consumption and sleep disturbances. Results: Both treatment modalities demonstrated similar levels of initial discomfort. There were no significant sex differences. Patients in the traditional fixed appliances group reported significantly (P < .05) greater discomfort than patients in the aligner group during the first week of active treatment. There was significantly more discomfort while chewing than when at rest. Traditional patients also reported significantly more discomfort than aligner patients after the first and second monthly adjustment appointments. Discomfort after the subsequent adjustments was consistently lower than after the initial bonding or aligner delivery appointments. A higher percentage of patients in the fixed-appliance group reported taking analgesics during the first week for dental pain, but only the difference on day 2 was statistically significant. Conclusions: Patients treated with traditional fixed appliances reported greater discomfort and consumed more analgesics than patients treated with aligners. This trial was not registered.
Article
Assessment of risk of bias is regarded as an essential component of a systematic review on the effects of an intervention. The most commonly used tool for randomised trials is the Cochrane risk-of-bias tool. We updated the tool to respond to developments in understanding how bias arises in randomised trials, and to address user feedback on and limitations of the original tool.
Article
Introduction: Our objectives were to assess patient satisfaction and quality of life among adults via 2 validated comprehensive questionnaires and to compare patient satisfaction and status in oral health-related quality of life immediately after orthodontic treatment in patients treated with Invisalign (Align Technology, San Jose, Calif) and those who received standard bracket-based treatment. Methods: Adult patients (n = 145) treated with bracket-based or Invisalign therapy were recruited from several private practices and a university clinic. The survey comprised a combination of the Dental Impacts on Daily Living index and the Patient Satisfaction Questionnaire. This 94-question assessment focused on various dimensions of satisfaction and quality of life. Multivariate analysis of variance and the bootstrap test were applied. A reliability analysis was used to assess responses at a 6-month follow-up for a small sample of patients. Results: Finally, 122 patients were assessed. The multivariate analysis of variance analysis showed that the eating and chewing dimension was significantly different between the 2 groups (Invisalign, 49%; bracket based, 24%; P = 0.047). No significant difference in any other satisfaction factors (all, P > 0.05) was identified. The follow-up assessment was only possible in a small sample of the bracket group; it showed adequate reliability values on the categories of oral comfort (intraclass correlation coefficient [ICC], 0.71), general performance (ICC, 0.755), situational (ICC, 0.80), and doctor-patient relationship (ICC, 0.75). Conclusions: Of the patients surveyed to assess their satisfaction and oral health-related quality of life immediately after completion of their orthodontic treatment, both the bracket-based and Invisalign treated patients had statistically similar satisfaction outcomes across all dimensions analyzed, except for eating and chewing: the Invisalign group reported more satisfaction. Patient satisfaction remained relatively similar 6 months later for the bracket-type treatment.
Article
Introduction: Our objective was to assess patient satisfaction and changes in oral health-related quality of life immediately after orthodontic treatment using the Invisalign system (Align Technology, Santa Clara, Calif). Methods: Adult patients were recruited from private practices in Canada and surveyed using a combination of 2 validated questionnaires: Dental Impact of Daily Living and Patient Satisfaction Questionnaire. This 94-question assessment focused on various dimensions of satisfaction and changes in quality of life. Multivariate analysis of variance, regression analysis, and canonical correlation analysis were applied in the data analysis. Results: A total of 81 patients, 29.6% men and 70.4% women, exclusively treated with the Invisalign system participated. The most significant improvements were seen in the appearance and eating and chewing categories, with patients responding positively to more than 70% of the questions in those categories. Food packing between teeth, affecting 24% of the participants, and pain affecting 16% were the most common sources of dissatisfaction. However, these negative experiences were not strong enough to reduce the overall positive experience that patients reported. Appearance and dentofacial improvement were strongly correlated. Canonical correlation of the Patient Satisfaction Questionnaire factors showed that doctor-patient relationship had a significant correlation with situational aspects, dentofacial improvement, and the residual category. Phrases from the doctor-patient relationship category such as "the orthodontist treated me with respect" and "carefully explained what treatment would be like" were associated with higher patient satisfaction. Conclusions: Although positive changes in appearance and eating categories were linked with patient satisfaction, doctor-patient relationship was the factor that correlated better with multiple aspects of patient satisfaction.
Article
Purpose: To investigate the impact of untreated malocclusion on different aspects of oral health-related quality of life (OHRQoL). Materials and methods: All relevant literature published up to February 18, 2016 was collected from nine electronic databases. To make studies comparable, studies that used the dental aesthetic index (DAI), index of orthodontic treatment need (IOTN), or index of complexity, outcome and need (ICON) to measure malocclusion and oral health impact profile (OHIP) to measure OHRQoL were selected for systematic review. Meta-analysis, two independent- samples t-test and binary logistic regression were used to test whether different malocclusion severity groups had different OHIP scores. Results: A total of 564 non-duplicate publications were identified first. Of these, 13 studies were included in this review. All studies had a cross-sectional design and most of them used convenience samples. Eleven studies presented a significant result about the association of malocclusion and OHIP scores. Statistical analyses showed that malocclusion had an impact on all subscales scores, and more severe malocclusion indicated higher OHIP scores on the subscales of physical disability, physical pain, psychological discomfort, psychological disability, and social disability. Conclusion: Untreated malocclusion was significantly associated with OHRQoL. The more severe the malocclusion, the worse was the impact on some physical domains and all psychosocial domains of OHRQoL. There was a lack of longitudinal population-based studies to confirm this result.